28 February 2014 Tunable dual-wavelength two-picosecond light source for coherent Raman scattering microscopy
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In narrow-bandwidth coherent Raman scattering (CRS) microscopy, efficient signal generation is accomplished with two-color laser sources providing synchronized picosecond pulses whose frequency difference and spectral widths match the molecular Raman frequency and bandwidth, respectively. With vibrational bandwidths of typically 10 cm-1, the optimum laser pulse durations thus correspond to about 2 ps. Here, we present a new light source consisting of an amplified Yb-fiber oscillator providing 2-ps pulses at 1031 nm and a synchronously green-pumped optical parametric oscillator (OPO). The OPO slightly shortens the pulses to < 2 ps while maintaining a bandwidth of 10 cm-1. Output power levels of 1 W in both the 1031-nm and the OPO-branch with continuously tunable frequency differences between the two beams covering a broad range from 700 to 4500 cm-1 are achieved. In addition to CARS microscopy, this light source allows for SRS imaging via an integrated electro-optical modulation of the 1031-nm beam at 20 MHz with a depth of >95%, locked to the laser repetition rate of 80 MHz. The OPO noise at 20 MHz was found to be only 60% above the combined detector and laser noise of a conventional Nd:YVO pump source. This represents a significant reduction in laser noise when compared to other fiber-based laser sources previously proposed for SRS microscopy. When SRS imaging with this new light is compared with a Nd:YVO pumped OPO (delivering 7 ps and 5 ps pulses, respectively), a 5- to 6-fold increase in SRS signal strength and signal-to-noise ratio has been achieved. Video-rate SRS and the capability of multi-spectral SRS imaging are demonstrated.
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Ingo Rimke, Ingo Rimke, Gregor Hehl, Gregor Hehl, Marcus Beutler, Marcus Beutler, Peter Volz, Peter Volz, Andreas Volkmer, Andreas Volkmer, Edlef Büttner, Edlef Büttner, "Tunable dual-wavelength two-picosecond light source for coherent Raman scattering microscopy", Proc. SPIE 8948, Multiphoton Microscopy in the Biomedical Sciences XIV, 894816 (28 February 2014); doi: 10.1117/12.2036358; https://doi.org/10.1117/12.2036358

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